1. Field of the Invention
The present invention relates to fuel supply systems used mainly for engines of vehicles.
2. Description of the Related Art
A known fuel supply system is disclosed, for example, in Japanese Laid-Open Patent Publication No. 2001-248512. The fuel supply system of this publication includes a fuel pump for supplying fuel stored within a fuel tank to a side of an engine, a pressure regulating valve for regulating the pressure of pressurized fuel supplied from the fuel pump to the side of the engine and for discharging surplus fuel, and a jet pump driven by a flow of the surplus fuel discharged from the pressure regulating valve. Typically, a general fuel pump is provided with a vapor jet (also known as a vapor escape hole or a vapor discharge hole, etc.) formed at a pump housing in order to discharge vapor that is generated within a pump passage due to the rotational movement of an impeller driven by a motor so that fuel vapor generated within the pump passage is discharged trough the vapor jet out of the pump while the fuel is pressurized.
However, the conventional fuel supply system disclosed in the above publication does not control discharge of fuel vapor through the vapor jet provided to the fuel pump. According to this construction, even if almost no vapor is generated when the pressure has been increased to a system fuel pressure (system fuel pressure is a fuel pressure within a fuel supply passage and is a normal fuel pressure level within a fuel supply system), i.e., at increasing pressure, pressurized fuel may be discharged through the vapor jet. As a result, a loss of flow of the pressurized fuel may be large and it may cause increase in load applied to the fuel pump. Further, because the jet pump is configured to be driven by the flow of the surplus fuel, it may cause a problem that the amount of fuel pumped by the jet pump may become instable due to the change of an amount of the surplus fuel.
Therefore, there is a need for a fuel supply system that can reduce a load applied to a fuel pump during increase of a system fuel pressure and can stabilize the amount of fuel pumped by a jet pump.